1. Field of the Invention
The present invention relates to user registration in a communication system.
2. Description of the Related Art
A diverse range of communication systems are in use today enabling communication between two or more entities, such as user equipment and/or other nodes associated with the system. Such systems may comprise, for example, communication of voice, data, and multimedia data.
Communication systems providing wireless communication for user terminals or other nodes are known. An example of a wireless system is a public land mobile network (PLMN). A PLMN is typically a cellular network wherein a base transceiver station (BTS) or similar access entity serves user equipment (UE) such as mobile stations (MS) via a wireless interface. The operation of the apparatus required for the communication is usually controlled by one or more control entities, which themselves may be interconnected. One or more gateway nodes provide for connecting the PLMN to other networks. Examples of other such networks are another cellular network, a public switched telephone network (PSTN) and packet switched data networks such as an IP (Internet Protocol) based network. The communication between the user equipment and the other elements of the communication system are based on an appropriate communications protocol, which defines the “rules” under which communication is handled in the system.
In the current third generation (3G) wireless system, there are defined various servers for the handling of different communication services for mobile users. These include servers that provide call state control functions, known as CSCFs. Control functions may also be provided by entities such as a home subscriber server (HSS) and various application servers (AS). The HSS is typically for permanently storing the user's (subscriber's) profile. For example, in the Release 5 architecture for 3G, as specified by the 3rd Generation Partnership Project (3GPP), these entities can be found located in the IP Multimedia Subsystem (IMS). Call state control function provides a serving function S-CSCF, an interrogating function, I-CSCF and a proxy function P-CSCF.
The IMS network may sit at the hub of the 3G architecture, supporting an IP based network that handles both traditional voice telephony and multimedia services. The 3GPP has chosen Session Initiation Protocol (SIP) as a core session signalling protocol for 3G networks. SIP has been developed by the Internet Engineering Task Force (IETF). The 3GPP specification 24.229 describing the IMS network basic operation from an SIP perspective can be found at http://www.3gpp.org/ftp/Specs/latest/Rel-5/24_series/24229-560.zip. It should be noted that SIP is a request/response style protocol, in the sense that for every message sent from a source, there is an associated response from the destination confirming receipt of the sent message.
Users are registered with S-CSCFs according to location and available communication links. The interrogating serving call state control function (I-CSCF) is used to contact the S-CSCFs. When the S-CSCF which is the assigned S-CSCF for a user cannot be contacted by the I-CSCF, it is possible to assign a new S-CSCF for a user during the registration procedure. When this is done, it is possible that the home subscriber server HSS receives a multimedia authentication request (MAR) command including an S-CSCF name which is not the same as the previously assigned S-CSCF for the user. In the existing 3GPP protocol, the home subscriber server can deregister the registrations in the old S-CSCF by using the Registration-Termination-Request (RTR) command. By assigning the reason NEW_SERVER_ASSIGNED to this command, this causes the user's public identity which is registered in the new S-CSCF to be deregistered from the old S-CSCF. A subsequent RTR command must then be issued for the rest of the user's public identities with the deregistration reason set to SERVER_CHANGE which causes the corresponding user data to be removed from the old S-CSCF and initiates a deregistration procedure for the user equipment UE to request the user equipment UE to re-register. The re-registration process is then directed by the I-CSCF to the new S-CSCF.
Thus, two individual command sets are required to implement the two necessary steps, that is the deregistration of the users' public identities from the previous S-CSCF and the re-registration of the public identities at the new S-CSCF.